Device formed using a hard mask and etch stop layer

ABSTRACT

A method of etching a device in one embodiment includes providing a silicon carbide substrate, forming a silicon nitride layer on a surface of the silicon carbide substrate, forming a silicon carbide layer on a surface of the silicon nitride layer, forming a silicon dioxide layer on a surface of the silicon carbide layer, forming a photoresist mask on a surface of the silicon dioxide layer, and etching the silicon dioxide layer through the photoresist mask.

This application is a continuation of prior application Ser. No.12/006,377, filed Dec. 31, 2007.

FIELD OF THE INVENTION

This invention relates to fabrication processes for semiconductordevices.

BACKGROUND

Silicon carbide (SiC) has a large energy band gap and high breakdownfield. As such, SiC is an attractive material for electronic devicesoperating at high temperatures and high power. SiC also exhibitsmechanical properties and chemical inertness which are useful inmicro-electromechanical systems (MEMS) as well as nano-electromechanicalsystems (NEMS) for applications in harsh environments. SiC based devicesare therefore particularly attractive for use as high-temperaturesensors and actuators.

Additionally, SiC has a high acoustic velocity and extremely stablesurfaces. Thus, SiC is a promising structural material for fabricatingultra-high frequency micromechanical signal processing systems. Thehighly stable physicochemical properties of SiC also improve theperformance of high-frequency resonators as the surface-to-volume ratioincreases when the resonator frequency scales into the GHz ranges.

One of the challenges in fabricating SiC devices is related to theselective etching of SiC films or SiC bulk materials. Unlike silicon(Si), SiC is not etched significantly by most acids and bases attemperatures less than about 600° C. Most wet etching processes,however, are not easily effected at temperatures greater than about 600°C. Non-standard techniques such as laser-assisted photo-electrochemicaletching have been developed, but such techniques require specialequipment and exhibit poor lateral dimension control.

Traditional fabrication processes incorporating photoresist etch masksare also problematic. Primary etch gasses that are used in SiC etchinginclude chlorine (Cl₂) and hydrogen bromide (HBr). The photoresistmaterial, however, exhibits poor selectivity compared to SiC whenexposed to traditional etch gases.

What is needed is a method of manufacturing a device incorporating amasking material which exhibits increased selectivity compared withtraditional masking materials. What is further needed is a method ofmanufacturing a device incorporating a masking material which exhibitsincreased selectivity when exposed to traditional SiC etching gases.

SUMMARY

In accordance with one embodiment of the present invention, there isprovided a method of etching a device that includes providing a siliconcarbide substrate, forming a silicon nitride layer on a surface of thesilicon carbide substrate, forming a silicon carbide layer on a surfaceof the silicon nitride layer, forming a silicon dioxide layer on asurface of the silicon carbide layer, forming a photoresist mask on asurface of the silicon dioxide layer, and etching the silicon dioxidelayer through the photoresist mask.

In accordance with another embodiment of the present invention, there isprovided a method of etching a semiconductor device including providinga substrate, forming an etch stop layer on a surface of the substrate,forming a silicon carbide layer on a surface of the etch stop layer,forming a hard mask layer on a surface of the silicon carbide layer,forming a photoresist mask on the hard mask layer, and etching thesilicon carbide layer through the hard mask layer and the photoresistmask.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a flow chart of an SiC etching portion of a process formanufacturing a device in accordance with principles of the presentinvention;

FIG. 2 shows a cross-sectional view of a substrate, which in thisembodiment is a SiC substrate, which may be used in a device inaccordance with principles of the present invention;

FIG. 3 shows a device including the substrate of FIG. 2 with an etchstop layer, which may include Si₃N₄, formed on the upper surface of thesubstrate;

FIG. 4 shows the device of FIG. 3 with a SiC layer formed on the uppersurface of the etch stop layer of FIG. 3;

FIG. 5 shows the device of FIG. 4 with a hard mask layer, which in thisembodiment includes SiO₂, formed on the SiC layer of FIG. 4;

FIG. 6 shows the device of FIG. 5 with a photoresist mask formed on theupper surface of the hard mask layer of FIG. 5;

FIG. 7 shows the device of FIG. 6 with the hard mask layer etchedbeneath the openings of the photoresist mask to expose portions of theupper surface of the SiC layer in accordance with principles of thepresent invention;

FIG. 8 shows the device of FIG. 7 with the SiC layer etched beneath theopenings of the photoresist mask to expose portions of the upper surfaceof the etch stop layer in accordance with principles of the presentinvention;

FIG. 9 shows the device of FIG. 8 with the etch stop layer etchedbeneath the openings of the photoresist mask to expose portions of theupper surface of the substrate in accordance with principles of thepresent invention;

FIG. 10 shows the device of FIG. 9 with the remainder of the photoresistmask removed to expose the remainder of the upper surface of the hardmask layer in accordance with principles of the present invention; and

FIG. 11 shows the device of FIG. 10 with the remainder of the uppersurface of the hard mask layer removed to expose the remainder of theupper surface of the SiC layer in accordance with principles of thepresent invention.

DESCRIPTION

For the purposes of promoting an understanding of the principles of theinvention, reference will now be made to the embodiments illustrated inthe drawings and described in the following written specification. It isunderstood that no limitation to the scope of the invention is therebyintended. It is further understood that the present invention includesany alterations and modifications to the illustrated embodiments andincludes further applications of the principles of the invention aswould normally occur to one skilled in the art to which this inventionpertains.

FIG. 1 shows a flow chart 100 of SiC etching portion of a manufacturingprocess for a device in accordance with principles of the presentinvention. The process 100 of FIG. 1 begins at step 102 and a substrateis provided at 104. At step 106, an etch stop layer is formed on thesurface of the substrate followed by formation of a SiC layer on theetch stop layer at the step 108. A hard mask is then formed on the SiClayer at step 110 and a photoresist mask is patterned on the hard maskat step 112.

Etching of the device begins with etching of the hard mask layer throughthe photoresist mask at the step 114. Next, the SiC layer is etched atthe step 116 through the photoresist mask and the hard mask layer. Theetch stop layer is then etched at the step 118.

When the desired etching is concluded, the photoresist mask is removedat the step 120 followed by the removal of the hard mask layer at thestep 122. The process then ends at the step 124. After the process shownin FIG. 1 is complete, further processing of the device may beperformed.

One example of the process of FIG. 1 is shown in FIGS. 2-11. A substrate130 is shown if FIG. 2. The substrate 130 may either be a SiC substrateor a substrate having a layer of SiC formed thereon. Next, FIG. 3 showsan etch stop layer 132 formed on the upper surface 134 of the substrate130. The etch stop layer 132 preferably includes silicon nitride(Si₃N₄). Next, a layer 136 of SiC is formed on the upper surface 138 ofthe etch stop layer 132 as shown in FIG. 4 and a hard mask layer 140 isformed on the upper surface 142 of the SiC layer 136 as shown in FIG. 5.The hard mask layer 140 in this embodiment includes silicon dioxide(SiO₂).

FIG. 6 shows a photoresist mask 144 in position on the upper surface 146of the hard mask layer 140. The photoresist mask 144 may be patterned toinclude a number of openings 148. The openings 148 may be of any desiredform such as circles, rectangles, etc. Portion of the upper surface 146of the hard mask layer 140 are exposed through the openings 148.

Etching of the device may then be performed using an etching gas whichpreferably includes Cl₂, HBr or both Cl₂ and HBr. The etching gascontacts the hard mask layer 140 through the openings 148 therebyetching the material directly beneath the openings 148 and generating avia 150 through the hard mask layer 140 to expose the SiC layer 136 asshown in FIG. 7.

Continued exposure to etching gases results in the etching of the SiClayer 136. The hard mask layer 140 is exposed to the etching gases aboutthe vias 150. The SiC layer 136, however, is more rapidly etched by theetch gases than the material used to form the hard mask layer 140. Inthe embodiment of FIGS. 2-11, the selectivity ratio of the SiC layer tothe SiO₂ hard mask layer is about 6:1. Accordingly, the predominanteffect of the etch gas is to extend the via 150 through the SiC layer136 to expose the upper surface 138 of the etch stop layer 132 as shownin FIG. 8.

Continued exposure to etching gases results in the etching of the etchstop layer 132. The selectivity ratio of SiC to the Si₃N₄ used in thisembodiment is about 1.4:1. Accordingly, the via 150 widens as the etchstop layer 132 is etched, particularly in the SiC layer 136. Etchingconcludes when the upper surface 134 of the substrate 130 is exposed tothe desired extent as shown in FIG. 9.

At this point, the photoresist mask 144 is no longer needed.Accordingly, any remnant of the photoresist mask 144 is removed usingany desired process leaving the remainder of the upper surface 146 ofthe hard mask layer 140 exposed as shown in FIG. 10. The remainder ofthe hard mask layer 140 is likewise removed using any desired processleaving the remainder of the upper surface 142 of the SiC layer 136exposed as shown in FIG. 11.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, the same should be considered asillustrative and not restrictive in character. It is understood thatonly the preferred embodiments have been presented and that all changes,modifications and further applications that come within the spirit ofthe invention are desired to be protected.

1. A semiconductor device, formed by a process comprising: providing asilicon carbide substrate; forming a silicon nitride layer on a surfaceof the silicon carbide substrate; forming a silicon carbide layer on asurface of the silicon nitride layer; forming a silicon dioxide layer ona surface of the silicon carbide layer; forming a photoresist mask on asurface of the silicon dioxide layer; and etching the silicon dioxidelayer through the photoresist mask using an etch gas which etchessilicon carbide at a higher rate than silicon dioxide.
 2. The device ofclaim 1, wherein etching the silicon dioxide layer through thephotoresist mask comprises: etching the silicon dioxide layer throughthe photoresist mask with an etch gas which etches silicon carbide at arate of at least about six times faster than silicon dioxide.
 3. Thedevice of claim 1, the process further comprising: etching the siliconcarbide layer through the etched silicon dioxide layer.
 4. The device ofclaim 3, wherein etching the silicon carbide layer comprises: etchingthe silicon carbide layer through the photoresist mask and through theetched silicon dioxide layer with an etch gas which etches siliconcarbide at a rate of at least about six times faster than silicondioxide.
 5. The device of claim 3, the process further comprising:etching the silicon nitride layer through the etched silicon carbidelayer.
 6. The device of claim 5, wherein etching the silicon nitridelayer comprises: etching the silicon nitride layer through thephotoresist mask, the etched silicon dioxide layer and the etchedsilicon carbide layer with an etch gas which etches silicon carbide at arate of at least about six times faster than silicon dioxide.
 7. Thedevice of claim 5, further comprising: removing the at least some of thephotoresist mask after etching the silicon dioxide layer.
 8. The deviceof claim 7, the method further comprising: removing the etched silicondioxide layer.
 9. A semiconductor device formed by a process comprising:providing a substrate; forming a silicon nitride etch stop layer on asurface of the substrate; forming a silicon carbide layer on a surfaceof the silicon nitride etch stop layer; forming a hard mask layer on asurface of the silicon carbide layer; forming a photoresist mask on thehard mask layer; and etching the silicon carbide layer through thephotoresist mask using an etch gas which etches silicon carbide at ahigher rate than silicon dioxide.
 10. The device of claim 9, whereinforming a hard mask layer on a surface of the silicon carbide layercomprises: forming a silicon dioxide layer on a surface of the siliconcarbide layer.
 11. The device of claim 9, wherein etching the siliconcarbide layer comprises: etching the silicon carbide layer through thephotoresist mask with an etch gas which etches silicon carbide at a rateof at least about six times faster than silicon dioxide.